In the Cretaceous there was 10 parts per mililon CO2 in the air. The planet had just formed – so there was loads of vulcanism. https://www.skepticalscience.com/co2-higher-in-past.htm
Then photosthesis formed, and we had the Permian. CO2 fell at the end of just1ppm – and life only recovered as animals evovled, to breath in the waste gas of plants -O2. http://www.biocab.org/carbon_dioxide_geological_timescale.html
In the Jurassic CO2 was at 4ppm, there was 65% more life on Earth than today. Sea levels were 60 meters LOWER http://www.livescience.com/44330-jurassic-dinosaur-carbon-dioxide.html
There were 3 natural ice-ages. With CO2 at 8ppm. http://www.natureworldnews.com/articles/18740/20151213/volcanic-event-triggered-ice-age-during-jurassic-period-researchers.htm
Even today, while photosynthesis limits global CO2 at 2ppm, it is at 4ppm over the poles. CO2 only rises in an ice age. Nature controls CO2. By burnign the Fossil Fuels, man has increased life on Earth – he can't affect the level of CO2 in the air. Photosynthesis on the land and seas caps CO2 at the modern level of just 2 parts per million.